The present invention generally relates to high speed connectors, and more particularly to a high speed edge card connector incorporating differential signal pair.
Many types of connectors are known in the art. One such type of connector is an xe2x80x9cedge cardxe2x80x9d connector that is used to provide an interconnection between a circuit board and another board that is commonly known in the art as a xe2x80x9cdaughter board.xe2x80x9d In order to achieve high density of terminals and provide more connections to more circuits, the terminals are placed close together on small pitches. In instances where the connector is used in high speed applications, crosstalk may occur between the signal terminals, which typically leads to signal error and degradation. It is important to minimize crosstalk in differential signal applications and to regulate the impedance of connectors used in terminating differential signal pairs.
In order to combat crosstalk and reduce signal interference, one solution known in the art is to provide at least one reference ground in close proximity to each signal terminal.
In conventional high speed connector applications, i.e., those capable of operating at 1.0 GHz and above, impedance is controlled by adding more conductive material to terminals, particularly to the ground terminals, in order to regulate the optimal impedance of the particular connector. This type of arrangement, is described in U.S. Pat. No. 5,853,303, issued Dec. 29, 1999, wherein the sizes and shapes of the terminals are manipulated to vary the overall capacitance of the terminals. In these type connectors, as illustrated in the ""303 patent, the terminals of the edge card connector are commonly arranged in a signal-ground-signal-ground, etc. (i.e., xe2x80x9cS-G-SGxe2x80x9d, etc.) order so that each and every signal terminal is positioned between two ground terminals.
The equation for determining impedance is generally accepted as Z{square root over (L/C)} where L=inductance, C=capacitance and Z=impedance, and given the preferred GS-G-S-G terminal arrangement stated above, each pair of signal and ground terminals act as a capacitor and thereby generate a capacitance during operation. This capacitance must be considered in determining the overall impedance of the connection. The capacitance for a system requires adding together all of the capacitances of the individual components of the connector system. As the system capacitance increases, the overall impedance of the system will drop. Likewise, as the system capacitance decreases, the overall impedance of the system will increase in that area. Drops in impedance occur along the edge card-connector interface as well as the connector-circuit board interface. It is desirable not to have widely varying rises and drops in the impedance of an edge card connector system, especially at the desirable high transmission speeds targeted for new and future electronic applications, in the order of 3 Gigahertz and greater.
Conventional solutions in the art for edge card connectors address only the decrease of the impedance as a design factor and no art, to applicant""s knowledge, seeks to increase the impedance of a connector system, by modifying the structure of the connector itself, in order to maintain the system impedance at the connector interfaces at 100 ohms, within tolerances. U.S. Pat. No. 6,433,286, issued Aug. 13, 2002 describes a means of increasing the impedance on a printed circuit board by forming a plurality of voids in a board ground reference plane and aligning signal traces with the pattern of voids. This is a complex solution and it requires extra expense in the design of the circuit board and mandates that a certain number of voids bu utilized with the circuit board. Additionally, if the signal traces are not aligned with the voids of the ground reference plane, the impedance modifying effects of the board layout will not be easily achieved.
The present invention is therefore directed to a connector system that overcomes the aforementioned disadvantages, both in the structure of the connector itself and in the structure of the circuit board.
Accordingly, it is a general object of the present invention to provide an improved edge card connector system that delivers a more regulated operational impedance level.
Another object of the present invention is to provide an improved edge card for use with a corresponding connector having a preselected operational impedance range, the edge card having a plurality of conductive traces formed along one edge thereof, the traces being arranged in a xe2x80x9ctripletxe2x80x9d pattern which includes two differential signal traces and an associated ground trace, each such triplet of traces being separated from other traces on the edge card by an interengaging space so as to spatially and electrically isolate each distinct trace triplet on the edge card for improved electrical performance.
A further object of the present invention is to provide an electrical connector for edge card applications, the connector having an electrically insulative housing with a card receiving slot extending longitudinally of the connector housing, the connector including a plurality of conductive terminals supported by the housing on opposite sides of the card-receiving slot, the terminals being arranged in xe2x80x9ctripletxe2x80x9d, or xe2x80x9ctriadxe2x80x9d grouping, each of which that include a pair of differential signal terminals and an associated ground terminal, the housing having a plurality of terminal-receiving cavities formed therein on opposite sides of the card-receiving slot, the terminals being arranged in said cavities in the distinct aforementioned triads, or triplets, each such grouping being separated by an intervening, empty terminal-receiving cavity such that each such terminal triad or triplet is supported by intervening space that is equivalent to two pitch or another spacing.
A still further object of the present invention is to provide a novel circuit board arrangement for use with an edge card connector, the circuit board having a plurality of conductive traces formed therein in a preselected pattern that defines a xe2x80x9cfootprintxe2x80x9d for an edge card connector, the footprint including an imaginary longitudinal axis defining a length of the connector housing and the vias disposed on opposite sides of the interengaging axis, the vias being arranged in patterns of triplets or triads that include a pair of differential signal conductive termination traces and an associated ground termination trace which lead to like circuits on the circuit board to which the connector may be mounted, the differential signal termination traces being spaced apart from each other, and further being spaced apart from the ground termination traces, the terminations traces being arranged in a triangular pattern when viewed from above the circuit board.
A further object of the present invention is to provide a ground reference plane associated with the aforementioned circuit board, the reference plane having a plurality of large non-conductive voids, or openings formed therein, each of which encompasses two of the circuit board vias in xe2x80x9claunchxe2x80x9d areas of the circuit board that make up a differential signal pair of vias, and the ground reference plane is connected to a third via that forms a ground via that is associated with the differential pair signal vias, the void decreasing capacitance between the differential signal vias and the ground plane to thereby increase the impedance in the circuit board launch area.
Yet another object of the present invention is to provide an improved edge card connector that is useful in differential signal applications and which operates with a preselected range of impedances in high speed signal applications, the connector having an elongated insulative housing and a slot formed therein that extends lengthwise of the housing, the connector further including a plurality of conductive terminals that are disposed in cavities formed in the housing on opposite sides of the slot, the terminals being arranged within the cavities in a repetitive pattern of signal xe2x80x9cAxe2x80x9d, ground, signal xe2x80x9cBxe2x80x9d, space, signal xe2x80x9cAxe2x80x9d, ground, signal xe2x80x9cBxe2x80x9d, space and so forth such that plurality of distinct triplets of terminals are defined in the connector by the intervening spaces, each of the triplets including an xe2x80x9cAxe2x80x9d and a xe2x80x9cBxe2x80x9d signal terminal and an associated ground terminal, the ground terminal being flanked on both sides by an associated signal terminal, the intervening spaces reducing the capacitive coupling between adjoining triplets.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.